Composite structures have been known in the art for many years. Although composite structures can be formed in many different manners, one advantageous technique for forming composite structures is a fiber placement or automated collation process. According to automated collation techniques, one or more ribbons of composite material (also known as composite strands or tows) are laid down on a substrate with a material placement machine. The substrate may be a tool or mandrel, but, can also be formed of one or more underlying layers of composite material that have been previously laid down and compacted.
Fiber placement processes typically utilize a heat source to assist in compaction of the plies of composite material at a localized nip point. In particular, the ribbon or tow of composite material and the underlying substrate are heated at the nip point to increase the tack of the resin of the plies while being subjected to compressive forces to ensure adhesion to the substrate. To complete the part, additional strips of composite material can be applied in a side-by-side manner to form layers and can be subjected to localized heat and pressure during the consolidation process.
Unfortunately, defects can occur during the placement of the composite strips onto the underlying composite structure. Such defects can include tow gaps, overlaps, dropped tows, puckers (i.e., raised regions in a tow), and twists. In addition, there are foreign objects and debris (FOD), such as resin balls and fuzz balls, that can accumulate on a surface of the composite structure which must be detected, identified and eventually removed from the ply surface.
Composite structures fabricated by automated material placement methods typically have specific maximum allowable size requirements for each flaw, with these requirements being established by the production program. Production programs also typically set well-defined accept/reject criteria for maximum allowable number of (i.e., density) of defects-per-unit area and maximum allowable cumulative defect width-per-unit area.
To ensure that the composite laminates fabricated by fiber placement processes satisfy the requirements pertaining to defect size, the structures are typically subjected to a 100% ply-by-ply visual inspection. These inspections are traditionally performed manually during which time the fiber placement machine is stopped and the process of laying materials halted until the inspection and subsequent repairs, if any, are completed. In the meantime, the fabrication process has been disadvantageously slowed by the manual inspection process and machine downtime associated therewith.
Recently, systems and methods have been developed that are capable of detecting, measuring, and marking individual defects in the composite structure. Exemplary systems and methods capable of accurately and reliably detecting, measuring and/or marking defects in a composite structure are disclosed in U.S. patent application Ser. No. 09/819,922, filed Mar. 28, 2001, entitled “System and Method for Identifying Defects in a Composite Structure”; U.S. patent application Ser. No. 10/217,805, filed Aug. 13, 2002, entitled “System for Identifying Defects in a Composite Structure”; and U.S. patent application Ser. No. 10/628,691, filed Jul. 28, 2003, entitled “Systems and Methods for Identifying Foreign Objects and Debris (FOD) and Defects During Fabrication of a Composite Structure.” The entire disclosures of U.S. patent application Ser. Nos. 09/819,922, 10/217,805, and 10/628,691 are each incorporated herein by reference as if fully set forth herein.
Systems and methods have also been developed which are capable of determining a defect characteristic representative of the composite structure, such as a defect density-per-unit area and/or cumulative defect width-per-unit area. Exemplary systems and methods capable of determining defect characteristics are disclosed in U.S. patent application Ser. No. 10/726,099, filed Dec. 2, 2003, entitled “Systems and Methods for Determining Defect Characteristics of a Composite Structure”, the contents of which are incorporated herein by reference as if fully set forth herein.
While the above-mentioned inspection systems and methods have worked well for their intended purposes and have reduced unproductive down time associated with inspection of laminate plies, the inventors hereof have recognized that repair of detected flaws is still very much a manual, labor-intensive process.